Loans - Wholesale Loan Portfolio - By Class of Receivable (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 928,887	$ 969,415	$ 947,651
Wholesale
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 437,507	$ 439,162	$ 423,837
% of total criticized exposure to total retained loans	1.55%	1.33%
% of criticized nonaccrual to total retained loans	0.34%	0.26%
Wholesale | Current and less than 30 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 435,059	$ 436,916
Wholesale | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	933	908
Wholesale | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	45	188
Wholesale | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	100,257	102,646
Wholesale | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	337,250	336,516
Wholesale | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	337,298	339,729
Wholesale | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	100,209	99,433
Wholesale | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	93,446	93,591
Wholesale | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	5,293	4,692
Wholesale | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,470	1,150
Wholesale | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 119,227	$ 129,806
% of total criticized exposure to total retained loans	4.22%	3.54%
% of criticized nonaccrual to total retained loans	1.08%	0.66%
Wholesale | Commercial and industrial | Current and less than 30 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 117,621	$ 128,678
Wholesale | Commercial and industrial | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	279	109
Wholesale | Commercial and industrial | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	36	168
Wholesale | Commercial and industrial | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	28,850	29,572
Wholesale | Commercial and industrial | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	90,377	100,234
Wholesale | Commercial and industrial | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	61,709	73,497
Wholesale | Commercial and industrial | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	57,518	56,309
Wholesale | Commercial and industrial | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	52,484	51,720
Wholesale | Commercial and industrial | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	3,743	3,738
Wholesale | Commercial and industrial | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,291	851
Wholesale | Real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 115,826	$ 115,737
% of total criticized exposure to total retained loans	0.75%	0.65%
% of criticized nonaccrual to total retained loans	0.06%	0.12%
Wholesale | Real estate | Current and less than 30 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 115,733	$ 115,533
Wholesale | Real estate | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	22	67
Wholesale | Real estate | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	6	3
Wholesale | Real estate | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	3,202	2,967
Wholesale | Real estate | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	112,624	112,770
Wholesale | Real estate | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	101,379	100,107
Wholesale | Real estate | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	14,447	15,630
Wholesale | Real estate | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	13,574	14,876
Wholesale | Real estate | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	808	620
Wholesale | Real estate | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	65	134
Wholesale | Financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 55,839	$ 47,648
% of total criticized exposure to total retained loans	0.40%	0.32%
% of criticized nonaccrual to total retained loans	0.04%	0.01%
Wholesale | Financial institutions | Current and less than 30 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 55,764	$ 47,622
Wholesale | Financial institutions | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	51	12
Wholesale | Financial institutions | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	2	10
Wholesale | Financial institutions | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	17,112	18,524
Wholesale | Financial institutions | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	38,727	29,124
Wholesale | Financial institutions | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	39,492	32,178
Wholesale | Financial institutions | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	16,347	15,470
Wholesale | Financial institutions | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	16,123	15,316
Wholesale | Financial institutions | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	202	150
Wholesale | Financial institutions | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	22	4
Wholesale | Governments & Agencies
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 13,111	$ 14,187
% of total criticized exposure to total retained loans	0.00%	0.01%
% of criticized nonaccrual to total retained loans	0.00%	0.00%
Wholesale | Governments & Agencies | Current and less than 30 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 13,097	$ 14,165
Wholesale | Governments & Agencies | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	13	18
Wholesale | Governments & Agencies | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1	4
Wholesale | Governments & Agencies | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	2,699	3,150
Wholesale | Governments & Agencies | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	10,412	11,037
Wholesale | Governments & Agencies | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	12,905	13,984
Wholesale | Governments & Agencies | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	206	203
Wholesale | Governments & Agencies | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	206	201
Wholesale | Governments & Agencies | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	0	2
Wholesale | Governments & Agencies | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	0	0
Wholesale | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 133,504	$ 131,784
% of total criticized exposure to total retained loans	0.47%	0.26%
% of criticized nonaccrual to total retained loans	0.07%	0.12%
Wholesale | Other | Current and less than 30 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 132,844	$ 130,918
Wholesale | Other | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	568	702
Wholesale | Other | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	0	3
Wholesale | Other | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	48,394	48,433
Wholesale | Other | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	85,110	83,351
Wholesale | Other | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	121,813	119,963
Wholesale | Other | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	11,691	11,821
Wholesale | Other | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	11,059	11,478
Wholesale | Other | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	540	182
Wholesale | Other | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 92	$ 161